Personally, I don't see anything wrong with buying bitcoin from somebody you know in real life. You just have to be smart about it. If you can't trust people you know, then how does it make sense to trust random strangers on the internet? Except it's an exchange P2P, you can buy stolen coins without knowing. The case will be even easier if you bought from someone you know, because the authorities can question both of you and dig down to the truth.
If it was online, where you don't know the person, how are you going to point to who you bought it from? ll you have your payment receipt and it's more difficult to locate the person because they have to go through a longer process. Sometimes, authorities that are not very thorough may just charge you with the crime instead of looking for the actual criminal.

You can land in trouble whichever way you choose. It's part of the risk of bitcoin.
I have a few things you could do to protect yourself to a certain level. One way is never to pay in cash. Let him send you his account number. If it's someone else's account number, don't accept it; ask for their own account number specifically. This is the way; there is a paper trail and proof that you paid for the bitcoin.
Secondly, since it's somebody you know, it shouldn't be hard to know if the person deals with bitcoin or not. It will be a little suspicious if somebody who doesn't care much about bitcoin and you guys don't talk about it comes up to sell you bitcoin. It may be nothing, but it's a red flag. For your own sake, ask casually how he got the bitcoin (depending on the kind of relationship you guys have, it may not be a weird question). This might also help you in court (if it gets that far) or if the authorities question you.

Again, pay attention to the red flags. Why is anybody selling bitcoin that he bought with his money and held for a long time at a discount? Why is a friend of yours reluctant to tell you how he got the bitcoin he's about to sell to you?
That's why I said you need to be smart about it.